5G Isn't Going Indoors Anytime Soon

A changing business model
The problem, of course, is that wireless network operators don't have the cash to build a wireless network inside every office complex, apartment building and warehouse in the country. Others had to step forward.

"The building owners decided, 'Well, I'll pay for it,'" said Edalgo of McKinstry. He said this is still a bit of a new concept and as a result there are a variety of payment models for in-building cellular networks, in terms of who pays and how much. He added that one of the new services that McKinstry now offers to building owners is financing for cellular networks, though Edalgo declined to provide details on the specifics of the offering.

Similarly, Djukic with Zinwave said his company could support a variety of financing mechanisms for in-building networks, and added that companies like NextEdge Networks and Strategic Venue Partners are beginning to step forward with financing specific to real estate companies and building owners looking to add wireless coverage in their locations.

Network operators are more than happy to have someone else pay to broadcast their signals inside of buildings. T-Mobile, for example, operates a program called BYOC (Bring Your Own Coverage), where the operator provides network design reviews, approvals and its signal source to building owners. Other US operators, such as AT&T, have similar programs.

5G is a whole new ball game
There's no doubt that wireless network operators are sighing in relief as building owners and others increasingly foot the bill for indoor networks. The problem though is that 5G indoors is a whole different animal.

"There's a whole new layer that you need for 5G," said ATIS's Anderson.

He explained that today's indoor DAS networks generally rely on low-band spectrum that propagates well. 5G, meantime, will likely heavily use millimeter-wave (mmWave) spectrum that can't travel through doors, glass, or around corners. That means any indoor 5G network in mmWave spectrum will probably need lots of antennas, pretty much everywhere, to cover every corner of every room. Anderson said an indoor 5G network in mmWave spectrum would probably need more antennas than even a high-powered WiFi network would.

And that, Anderson said, means that most indoor 5G networks will have to use a "neutral host" design so that the building owner won't have to install different antennas for each wireless provider. Instead, 5G operators will all have to "share" a building's network equipment so that the network inside the building can connect both AT&T and Verizon customers, for example.

So far, Anderson explained, there are no standards specifically designed for indoor 5G mmWave networks using a neutral host model. However, he said that there are plenty of related technologies that can be applied to the situation, such as roaming and MOCN (Multi Operator Core Network), a 3GPP standard that allows several operators with different core networks to share common RAN nodes.

But Anderson said the industry has a long way to go before it can apply those technologies to indoor 5G. For example, he said that ATIS recently penned a white paper outlining the various ways US wireless operators could potentially support neutral host 5G networks indoors -- meaning, there isn't even a standard yet for neutral host 5G networks. The industry is only in the very early stages of outlining the contours of the problem and potential solutions and hasn't even gotten to the part where companies can evaluate actual technological solutions.

That isn't stopping some of the industry's biggest vendors from talking up the 5G indoor opportunity. Ericsson, for example, said it tested its 5G small cells with Swisscom in Switzerland in an indoor setting. "Our 5G Radio Dot allows service providers to reuse existing indoor network infrastructure as they upgrade from 4G. Building on the existing Radio Dot System architecture, one can upgrade and complement existing networks quickly and efficiently," boasted Martin Buerki, head of Ericsson Switzerland, in a release from the company.

Qualcomm, too, has started discussing the issue. The company argued that the propagation characteristics of 5G in mmWave spectrum is a benefit, not a drawback. "The fact that mmWave does not propagate well from the outside to inside is beneficial for deploying mmWave indoors as well, since the same mmWave spectrum can be reused indoors with limited coordination with the outdoor deployment," Qualcomm wrote in a recent blog.

Much of this in-building coverage discussion centers on 5G in mmWave spectrum. As operators like T-Mobile and AT&T launch 5G in the low-band spectrum, they'll undoubtedly craft marketing messages around their new ability to push 5G into more indoor locations. They likely won't mention that low-band 5G won't perform like mmWave 5G.

Back in the real world, it's still about coverage
All that said, 5G isn't even on the radar of most building owners in the US, at least today.

"We're just now seeing the design requirements from the carriers hit 4.5G levels" in buildings, said McKinstry's Edalgo, explaining that advanced LTE technologies like LAA and carrier aggregation are only now making their way into operators' in-building plans.

Edalgo added that, among building owners, there's no demand for 5G right now.

Zinwave's Djukic said he's hearing the same sorts of comments from his customers. He said discussions with building owners today are all about 4G and coverage, not 5G and capacity.

Wall Street analysts aren't expecting 5G to give Boingo a major boost anytime soon. "Keep in mind, [DAS] upgrades aren't entirely dependent on the timing of any ramp in 5G spending," wrote the analysts at Jefferies in a recent note to investors. "Boingo is actually still in the process of upgrading some venues from 3G to 4G."

In indoor environments with obstacles that do not completely block the transmition (these would be concrete, chicken-wire, metals, water, etc), the remaining transmitted signal depends on electrical conductivity of obstacles, and is mostly affected by losses described best by skin-effect formulas -- which are given/approximated by the square root of the frequency.

Interestingly enough, it turns out that specific "lower"-frequency ranges can as well be approximated by the square root, even in obstacle-free spaces, and the approximation aligns well with empirical measurements (in indoor environments).

Re: Data on 5G IndoorFormally correct, I should have stated that the attenuation coefficient is roughly proportional to the square root of frequency (no, not the square of frequency). BTW, the Friis formula was shown to be an antenna effect and not a wave-propagation effect (for example, see https://www.dsprelated.com/showarticle/62.php).

The dependence on square root of frequency is valid for any propagation medium with non-zero conductivity, i.e. for everything but vacuum. If you are tempted to argue that (dry) air is close to that, I will come back with adding a few obstacles (such as wood, concrete, anything with metal or presence of water) into the model, and point you to the calculation of strength of non-absorbed (propagated through obstacles) signal -- which will be eventually closely dependent on "remainders" after skin effect-related losses.

Re: Data on 5G IndoorIt appears that indoor 5G will follow the way Wi-Fi had to walk: shifting from 2.4 GHz to 5 GHz brought more frustration than benefits. Simple physics tells that propagation decreases roughly with the square root of frequency (more or less, add or take a water peak or two), and operation at millimeter waves decreases the reach/coverage even further.

I assume that in a few years, we'll start hearing about "mesh 5G" -- analogous to mesh Wi-Fi -- as the only way to guarantee proper indoor coverage and performance. (Just remember I used this term first. :)

I am also pretty sure that the debate about health implications will heat up (finally). One does not have to have a PhD in physics to understand that signal attenuation translates to absorption -- in walls, water tanks, our pets and our bodies.